A belt retractor with the above characteristics is described in DE 196 81 341 C1. Since it is necessary to couple the belt spool shaft and the profile head during normal winding up and out, and also during normal belt locking, two shear pins are arranged on the side of the belt spool shaft which faces the profile head, which engage with corresponding apertures in the profile head and which are riveted to the profile head during assembly, so that belt spool shaft and profile head are held together as one assembly. If a great tensile force is exerted on the belt in the direction in which the belt is pulled out following locking of the belt shaft initiated by the belt/strap/sensitive or vehicle/sensitive control system, for example because of a vehicle collision, the shear pins break off, and the belt spool shaft can afterwards be rotated relative to the locked profile head in the direction in which the belt is being pulled. This relative rotation is taken up by the torsion bar which comes into play between the belt spool shaft and profile head, which provides the desired force limitation based on the torsional deflection of the torsion bar.
The known belt roller is associated with the disadvantage that manufacture of the shear pin connection is costly and time-intensive, because the shear pins which engage in the recesses of the profile head are riveted to the profile head, whereby and high demands are placed on the precision of the connection and fit of these components. The force peak which occurs as a result of the shearing off of the shear pins immediately before the force limitation takes effect is difficult to define or to set, and finally, following shearing of the shear pins, axial forces are no longer restrained, whereby the torsion bar elongates in the axial direction when subject to torque due to plastic deformation and drives belt spool shaft and profile head axially apart, which is not desirable.
An object of this invention is to improve the connection between belt spool shaft and profile head in a self-locking belt roller of the type previously described with regard to its manufacture and function.